Mitochondria and chloroplasts are self-reproducing organelles in the cytoplasm of cells. They contain DNA molecules bearing a small but important set of genes; these genes play major roles in the control of cellular energy metabolism (oxidative phosphorylation, electron transport, and photosynthesis). The genes are inherited according to rules quite different from the Mendelian laws which govern the behavior of nuclear genes. The objectives of this project are: (1) to add to our knowledge of the unique phenomena of organelle transmission genetics, and (2) to learn more about the behavior of organelles and organelle DNA at the cellular and molecular levels, and use molecular levels, and use this information to explain the special rules of transmission genetics. In this way we hope to add the fund of knowledge about basic aspects of both genetics and cell biology, and lay the groundwork for future studies of the evolutionary genetics of mitochondria and chloroplasts. Specifically, the proposal describes experiments to study the size of the populations of organelles and organelle genes within single cells; the mixing and recombination of organelle DNA molecules from the two parents within single cells; the mixing and recombination of organelle DNA molecules from the two parents within zygotes; the replication of the DNA molecules; especially the preferential replication of DNA from one parent; and the distribution of organelles and DNA to daughter cells during cell division. Most experiments use yeast for studies of mitochondria and Chlamydomonas for chloroplasts. Important new methods to be employed include restriction fragment analysis of directly determine the ratios of mitochondrial DNA molecules of different genotypes at various time during a cross; the use of cdc mutants which specifically block one or another of the processes being studied in yeast; and the selection and analysis of mutants which modify organelle transmission genetics. Information about the behavior of organelles and their DNA at the cellular and molecular levels will be used to explain the unique aspects of organelle gene inheritance: biased transmission of genes from one parent; uniparental inheritance (loss of genes from one parent in zygotes); zygote heterogeneity and the random drift of gene frequencies; and the vegetative segregation of organelle genes.